Early attempts to synthesize .alpha.-amino acids or derivatives thereof by reacting a Schiff base or a nitrile with carbon monoxide and hydrogen were unsuccessful. [Bull. Chem. Soc. Japan 33 (160) 78]
U.S. Pat. No. 3,766,266 to Wakamatsu discloses a method of producing an N-acyl-.alpha.-amino acid which comprises holding an aldehyde, an amide of a carboxylic acid and carbon monoxide at a temperature of 10.degree. to 300.degree. C. and a pressure of at least 500 atm. in the presence of a carbonylation catalyst until said N-acyl-.alpha.-amino acid is formed.
In Chem. Comm. 1540 (1971), Wakamatsu, et al. disclose a cobalt-catalyzed reaction which gives various N-acyl amino-acids from an aldehyde, an amide and carbon monoxide. In this disclosure, while benzaldehyde was used as the starting aldehyde, there was no corresponding .beta.-phenyl-substituted amino acid obtained. Instead of the expected amino acid product, a imine was obtained by a simple "amination" reaction.
An article by Parnaud, et al., in Journal of Molecular Catalysis, 6 (1979) 341-350, discusses the synthesis potential and the catalytic mechanism for the reaction wherein N-acyl-.alpha.-amino acids are produced by reacting an aldehyde, CO and an amide in the presence of dicobalt octacarbonyl.
In amidocarbonylation, the aldehyde can be generated in situ from allyl alcohol, alkyl halides, oxiranes, alcohols and olefins followed by the reaction with an amide and carbon monoxide to produce an N-acyl-.alpha.-amino acid.
A related Patent, U.S. Pat. No. 3,996,288 discloses that when an alcohol or certain of its ester derivatives is held at 50.degree. C. to 200.degree. C. and 10 to 500 atm. in the presence of hydrogen, carbon monoxide, the amide of a carboxylic acid and a carbonylation catalyst, an aldehyde having one more carbon atom than the alcohol or ester is formed in good yield. If the amide has at least one active hydrogen atom on its amide nitrogen, it further reacts with the aldehyde and carbon monoxide to form an N-acyl-amino acid.
Hirai, et al. discuss a process for combining the transition metal catalyzed isomerization of allyl alcohol to aldehyde and cobalt catalyzed amidocarbonylation to provide a route from allylic alcohols to N-acyl-.alpha.-amino acids. See
Tetrahedron Letters, Vol. 23, No. 24, pp. 2491-2494, 1982.
U.S. Pat. No. 4,264,515 by R. Stern et al. discloses a process for obtaining terminal N-acyl-.alpha.-amino acids by a reaction catalyzed by a cobalt carbonylation catalyst wherein the aldehyde is produced in situ from olefins and CO/H.sub.2 mixtures. An unsaturated vegetable oil or C.sub.8 -C.sub.30 monoolefinic compound is reacted with an amide, carbon monoxide and hydrogen in the presence of a cobalt catalyst. The process is operated in one step and provides for increased selectivity.
A recent review article, published by Ojima in Journal of Organometallic Chemistry, 279 (1985), 203-214, discussed the synthesis of N-acetyl-.alpha.-amino acids from (a) the isomerization-amidocarbonylation of allylic alcohols, (b) the isomerization-amidocarbonylation of oxiranes and (c) the hydroformylation-amidocarbonylation of trifluoropropene. The hydroformylation-amidocarbonylation of trifluoropropene in Ojima's work demonstrated a surprising regioselectivity for products 1 and 2. ##STR1##
The results demonstrated in that work showed the highly regioselective synthesis of N-acetyltrifluorovaline (1) (94%) and N-acetyltrifluoronorvaline (2) (96%) in high yields by using Co.sub.2 (CO).sub.8 --Rh.sub.6 (CO).sub.16 and Co.sub.2 (CO).sub.8 as catalysts respectively. The results showed the surprising difference in yield when using Co.sub.2 (CO).sub.8 as opposed to Co.sub.2 (CO).sub.8 --Rh.sub.6 (CO).sub.16 catalysts in the special case of the fluoroolefin substrate.
The use of amidocarbonylates reactions in substrates containing a functionality such as ester group (that is, methyl or ethyl acrylate) in one step to produce the corresponding monoester of the N-acetylglutamate has not been previously disclosed. In a British patent specification No. 828,946 (1960) titled "Synthetic Process for Producing Glutamic Acid From Acrylonitrile", the reaction involved the hydroformylation of acrylonitrile followed by hydrocyanic acid and ammonia reaction in two steps. In a related patent, U.S. Pat. No. 3,766,266, a two-step synthesis from acrylate to aldehyde is disclosed, followed by the reaction of acetamide and carbon monoxide to produce the corresponding final product, glutamic acid. The reaction conditions in the two separate steps are slightly different.
The present invention involves the use of Bis-1,3-(diphenylphosphino)propane in combination with dicobalt octacarbonyl to achieve the conversion of acrylate into glutaric acid derivatives in a single step. K. Murata et al reported earlier the effect of Di(tertiary phosphine) ligand in hydroformylation of methyl acrylate. (Bull. Chem. Soc. Jpn., 53, 214-218 (1980). The reaction rate was related to the species of bidental phosphine ligand and Co-P ratio. J. Molecular Catalysis 23 (1984), 121-132 and Chem. Commu. (1979) 785, have reported the similar results in CO/H.sub.2 O reactions. However, J. Organometallic Chem. 1985, 283, No. 1-3, reported that HCo(CO).sub.2 (Bu.sub.2 PCH.sub.2 CH.sub.2 PBu.sub.2) was found to be an inactive catalyst for olefin hydroformylation and required an activation period.
The results of the instant invention using Co.sub.2 (CO).sub.8 with a bis-phosphine ligand in a one step synthesis are novel in the following respects:
(1) The presence of 1,3-bis-diphenylphosphino propane stabilizes dicobalt octacarbonyl and allows the reaction to proceed predictably at a low temperature in comparison with dicobalt octacarbonyl alone.
(2) The combined Co.sub.2 (CO).sub.8 and bis-phosphine ligand catalyst performs the reaction under milder reaction conditions, for example, as low as 800 psi.
(3) Rhodium species used in the comparative example affects regioselectivity.
Previous methods known in the art for preparing glutamic acid involve two steps. It would be an advance in the art to devise an inexpensive, one-step method of making glutamic acid in high yields with a great degree of linearity under mild conditions from an acrylate, an amide and syngas.
The instant invention relies on a cobalt catalyst system for the synthesis of glutamic acid from methyl or ethyl acrylate, acetamide and syngas wherein yields of glutamic acid are as high as 80% and a linearity of .about.80% is observed using very mild reaction conditions. After the ester intermediate is obtained, extraction by a acid/base medium such as Na.sub.2 CO.sub.3 or H.sub.3 PO.sub.4 are used to obtain the glutamic acid in good yield.